In recent years, UV- (ultraviolet-) LEDs have started to appear on the market. Quartz glass is generally used for encapsulating UV-LEDs. However, quartz glass is expensive, and suffers from another problem in that the UV light extraction efficiency is low due to the refractive index. As a result, the encapsulating of UV-LEDs with resins such as epoxy resins and addition reaction-type silicone resins is now being investigated. However, when UV-LEDs are encapsulated with these types of resins, problems including low UV light transmittance and severe resin degradation tend to occur.
Encapsulating materials that use a condensation-type silicone resin have been proposed as silicone-based encapsulating material compositions capable of addressing the above problems. For example, a silicone-based encapsulating material composition containing: a bifunctional thermosetting silicone resin (A), a multifunctional thermosetting silicone resin (B), and a curing catalyst (C), wherein (A) and (B) are immiscible at 80° C., has been proposed (see Patent Document 1).
In the silicone-based encapsulating material composition of Patent Document 1, because (A) and (B) are immiscible at 80° C., (A) and (B) undergo phase separation in a melted system, and because the density of (B) is higher than the density of (A), the component (B) tends to settle down through the liquefied encapsulating material composition and accumulate in the vicinity of the bottom lead electrodes, and when subjected to a high-level crosslinking reaction, covers the surface of the lead electrodes with a layer having superior gas barrier properties.